In Longworth’s thoroughly delightful fourth Provençal mystery (after 2013’s Death in the Vines), examining magistrate Antoine Verlaque and Marine Bonnet, his law-professor girlfriend, take a vacation on Sordou, a small island off the coast of Marseilles. They stay at the Locanda Sourdou, a newly reopened hotel that retains its 1960s elegance. Fellow guests include Sylvie Grassi, Martine’s best friend; Eric Monnier, an elderly poet; Bill and Shirley Hobbs, an American couple; and over-the-hill actor Alain Denis, whose rudeness upsets everyone, especially his sensitive teenage stepson. When one of their company is shot to death, Antoine must move into professional mode. Longworth deftly handles what is in effect a locked-room mystery, but the book’s real strength lies the backstories she creates for each of the distinctive characters. The puzzle’s answer, buried in the past, is well prepared by what has come before.